Process for reducing the acidity of hydrocarbon mixtures

ABSTRACT

Process for reducing acidity in hydrocarbon mixtures, through thermal treatment of hydrocarbon streams, such as petroleum products, fractions and its derivatives, in the presence of a spent hydrorefinery catalyst, in other words, that has already been used in the Hydrotreatment units (HDT) of a refinery.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon, claims the benefit of, priority of, andincorporates by reference, the contents of Brazilian Patent ApplicationNo. PI 0403556-9 filed Aug. 26, 2004.

SCOPE OF THE INVENTION

The scope of the invention for the present application is found amongprocesses to reduce the acidity of hydrocarbon mixtures. Preferably,within the processes that involve treatment of hydrocarbon mixtures suchas, for example, petroleum products, their fractions and derivatives, inthe presence of compounds capable of reducing the acid concentration insaid mixtures.

DESCRIPTION OF THE STATE OF THE ART

Newly discovered oil reservoirs possess characteristics that are quitepeculiar. The predominance of heavy fractions with high content ofcontaminants and acidity has been a challenge for petroleum processingcompanies, in the sense of being able to rapidly adapt processing unitsto the new qualities of petroleum streams. The adequacy of industrialunits as well as pipes and metal equipment is dependent on thedistribution of naphthenic acids in petroleum fractions. Thisdistribution is subject to change such as the processing of petroleumstreams coming from the new wells.

The high acid content not only affects the processing of petroleumproducts and their fractions but also influences the marketing of crudeoil. Currently, it is known that the market devalues the price of rawmaterials in an amount ranging between US$ 0.50 and US$ 0.70 per barrelper unit with a total acid number (TAN) of over 0.5 mg KOH/g of oil.

Furthermore, with the increase in the production of heavier oils, itmakes it that much more problematic to separate water/oil emulsions. Thepolar character of carboxyls present favors the formation of emulsionsthat reduce the efficiency of the desalting stage of petroleum.Therefore, reducing acidity is a critical stage not only in terms ofcosts, but also in the refining process.

Some patents protect processes for reducing the acidity of petroleum andderivatives. One of the first approaches would be to use oil mixtureswith different levels of acidity.

The application of corrosion inhibitors is another solution used to workaround the problem of acidity. In this vein, the North American patentU.S. Pat. No. 5,182,013 contends that organic polysulphides areinhibitors effective against corrosion caused by naphthenic acids inrefinery distilling units.

North American patent U.S. Pat. No. 4,647,366 recommends adding analkynediol and a polyalkylene polyamine as inhibitors to naphtheniccorrosion.

Acidity may be reduced even by treating oil with alkaline solutions ofsodium hydroxide or potassium hydroxide, as discussed in North Americanpatent U.S. Pat. No. 4,199,440. However, this approach demands the useof very concentrated alkaline solutions. In this case, the formation ofemulsions that cause separation difficulties is a critical point.Therefore this solution would be applicable only for low basicconcentrations.

Treatment with a calcium sulphonate or naphthenate based alkalinedetergent is recommended in North American patent U.S. Pat. No.6,054,042 to work around the problem of emulsions. The oil is treated attemperatures between 100° C. and 170° C. with stoichiometric proportionsof calcium for acid functionality in the oil of close to 0.025:1 up to10:1 moles, or 0.25:10:1, or other proportions.

The North American patent U.S. Pat. No. 6,258,258 recommends the use ofpolymeric amines, such as polyvinyl pyridine, with the purpose ofreducing acid content of petroleum.

Patent U.S. Pat. No. 4,300,995 recommends treatment of carbon andliquids obtained from carbon, coming from vacuum gas oil and petroleumsediment that introduce acidic functionalities, with alkaline solutionsof quaternary ammonium hydroxides in alcohol or water, such as hydroxideof tetramethylammonium.

International patent WO01/79386 uses an alkaline solution with group IA,IIA metal and ammonium hydroxides and the application of a transferagent such as, for example, non-alkaline quaternary salts andpolyethers. North American patent U.S. Pat. No. 6,190,541 already usesbases and/or phosphates with an alcohol.

In North American patent U.S. Pat. No. 6,086,751, naphthenic acidity isreduced through the application of a thermal treatment. The oil isinitially submitted to a heating process in a reactor with a short dwelltime to remove water and then is submitted to temperatures of between340° C. and 420° C., with a pressure lower than 100 psig and reactiontimes of up to 2 hours.

In the North American patent U.S. Pat. No. 5,985,137, the naphthenicacidity and the sulphur content of the oil are reduced through thereaction with alkaline-earth metal oxides, forming neutralized andalkaline-earth metal sulfide compounds. The temperature must be higherthan 150° C. to remove the carboxylic acids and higher than 200° C. forthe sulphide salts to form. The pressure applied must keep the materialfrom vaporizing. In general, the majority of the methodologies forreducing naphthenic acidity involving thermal treatments with or withoutthe addition of alkaline solutions demand the application ofsurfactantes to work around the problem of emulsions.

Another approach is the adsorption of the naphthenic acid throughadsorbent compounds with catalytic properties, under temperaturesbetween 200° C. and 500° C., followed by the recovery of the relatedadsorbent agent. North American patent U.S. Pat. No. 5,389,240 describesa process for removing naphthenic acids from petroleum streams likekerosene in the presence of a material related to Hydrotalcite calledMOSS (“metal oxide solid solution”) in combination with a sweeteningprocess. In order for the material to be adequate for the objectives ofthe patent, it must be calcinated at about 400° C. The inventiondisclosed is applicable to streams with extremely reduced naphthenicacid content, with TAN range of 0.01 mg KOH/g of oil to 0.06 mg KOH/g ofoil, and may reach up to 0.8 mg KOH/g of oil.

North American patent U.S. Pat. No. 6,027,636 protects the process ofelementary sulphur removal and sulphurous contaminants present inrefined petroleum products through contact of the fluid containingmercaptans through an adsorbent selected from one of the following:Baierite, Brucite and derivatives of Hydrotalcite.

The use of a hydrotreatment catalyst for the reduction of naphthenicacidity is mentioned in North American patent U.S. Pat. No. 5,871,636.Said patent refers to the use of a VIB and VIIIB transition metalsulphide catalyst, supported in alumina. For example, a cobalt andmolybdenum catalyst (KF-756 created by Akzo-Nobel), supported in amatrix of porous alumina with a surface area within a range of between100 to 300 m²/g which has been sulphonated prior to use. By using thispatent in an absence of hydrogen, a maximum reduction of naphthenicacidity of 53% in crude oil having an initial TAN of 4 mg KOH/g of oilis achieved.

In spite of advances in the state of the art in processes to reduceacidity in hydrocarbon mixtures, it is still necessary to develop aprocess that is more efficient, with lower cost and that minimizesemulsion formation, in order to facilitate the separation of theproducts.

SUMMARY OF THE INVENTION

The process of reducing acidity in hydrocarbon mixtures, which is theobject of this invention, attempts to eliminate partially or wholly theabove mentioned drawbacks, through thermal treatment of hydrocarbonstreams, such as petroleum products, fractions and its derivatives, inthe presence of a spent hydrorefinery catalyst, in other words, that hasalready been used in the Hydrotreatment units (HDT) of a refinery.

Before or after desalting, the stream of hydrocarbons to be treated isheated first. After the heating stage, said stream is placed in contact,continually, with a fixed bed of spent catalyst from the HDT, withoutusing hydrogen. The pressure must be such that, after the treatment, thestream should be at the normal pressure of the downstream system(desalting or atmospheric distillation). Finally, the treated streamcontaining a reduced value of TAN follows the conventional flow of oilrefining process and the spent catalytic is discarded by the usualmethod used in conventional Hydrotreatment units.

BRIEF DESCRIPTION OF THE ILLUSTRATIONS

The process to reduce acidity in hydrocarbon mixtures, the object of thepresent invention, will be better understood through the descriptiongiven below, with example headings, together with the drawings below,which are an integral part of the present report.

FIG. 1 shows a solution for the treatment of hydrocarbon mixtures afterpassing through the desalting unit, in accordance with the presentinvention.

FIG. 2 shows a solution for the treatment of hydrocarbon mixtures beforepassing through the desalting unit, in accordance with the presentinvention.

FIG. 3 shows a table of TAN x reaction time that illustrates thereduction of the TAN according to the process of reducing aciditydescribed in this report.

DETAILED DESCRIPTION OF THE INVENTION

The process proposed in this invention is founded in the reactionbetween organic acids and the surface of the spent catalyst, alreadyused in the HDT units, which in other instances was considered asindustrial refuse. In this way, the process proposed offers andalternative application for the spent HDT catalyst, considered today tobe refuse of extremely low value, a pollutant and hazardous wastematerial.

The present invention refers to a process to reduce naphthenic acidityof hydrocarbon mixtures such as, for example, petroleum products, theirfractions and derivatives that contain TAN that fall within a range ofbetween 1 and 10 mg KOH/g of oil, preferably with TAN that falls withina range of between 1.5 and 8 mg KOH/g of oil, through a thermaltreatment in the presence of a spent catalyst from a Hydrotreatmentunit. Spent catalyst is understood to mean the catalyst or mixture ofcatalysts already used in HDT units in a refinery. The referredtreatment promotes a reduction of TAN in the load of up to 98%.

The stages of the process include:

-   -   Heating the hydrocarbon mixture to be treated at temperatures        that fall within a range of between 240° C. and 400° C., before        or after desalting, with said hydrocarbon mixture presenting        high levels of naphthenic acidity.    -   Placing in contact, continually, said hydrocarbon mixture with a        fixed bed of spent catalyst coming from a Hydrotreatment unit,        at a temperature within the range of 270° C. and 350° C.,        preferably, at a temperature within the range of 270° C. and        350° C. The pressure must be such that, after the treatment, the        hydrocarbon mixture should be at the normal pressure of the        downstream system (desalting or atmospheric distillation). The        space velocity in the reactor falls in a range of between 0.25        h⁻¹ and 10 h⁻¹, preferably within a range of between 0.5 h⁻¹ and        4 h⁻¹. The catalyst used in this invention is refuse or a        mixture of discarded catalysts from Hydrotreatment units, made        of transition metals (Co—Mo, Ni—Mo, etc), supported in        refracting oxides that may be chosen from any one of the        following: alumina, silica, titanium, zirconium and/or mixtures,        among others. The spent catalyst may or may not go through an        intermediary stripping stage in the presence of an inert gas;    -   Continual withdrawal of the treated hydrocarbon mixture        containing a reduced TAN value for later processing in        conventional petroleum refinery units; and    -   Disposal of the catalyst at the end of the campaign time, in the        usual way used in conventional Hydrotreatment units.

In a typical petroleum refining process, the petroleum, after thethermal exchange with other refinery streams, is sent for desalting andlater to a preflash tower to separate the majority of lighter products.The present process to reduce naphthenic acidity of petroleum productsand derivatives containing high levels of TAN may be implemented beforedesalting or after the preflash tower.

The option to implement the oil treatment process after the desalting isshown in FIG. 1. The petroleum stream treatment takes place through thefollowing stages:

-   -   the liquid effluent (3) from the preflash tower (2) is at a        temperature between 260° C. and 280° C. and is transported        towards the furnace (4) that raises the temperature of the        effluent to a temperature that when it leaves the fixed reactor        bed (trickle bed) (6) it will be approximately equal to the        normal temperature of a load from the atmospheric distillation        tower (8);    -   the effluent (5) from the furnace (4) is then injected into the        top of a fixed bed reactor (trickle bed) (6). In this reactor,        the stream flows downward and comes into contact with the heated        catalyst, where the removal of the naphthenic acids then occurs;        and    -   the treated stream (7) is transported to the atmospheric        distillation tower (8) that operates in the conventional manner.

The option of processing the petroleum treatment before desalting offersan additional benefit of increasing the probability of breaking down theemulsions, as the hydrocarbon mixtures have their naphthenic acidityreduced. In this case, the non-treated hydrocarbon mixture must beheated additionally with a treated hydrocarbon mixture, so that thenon-treated hydrocarbon mixture will rise in temperature andconsequently reduce the temperature of the treated hydrocarbon mixturebefore entering the desalter. To complete heating so that the reactivetemperature necessary for treatment is reached, a furnace should beinstalled before the reactor.

An example of one possible solution is shown in FIG. 2 for the petroleumacidity reduction process. This would be implemented before going to thedesalting unit. In this case, said treatment takes place through thefollowing stages:

-   -   the non-treated petroleum stream (9), coming from the preheating        system, enters into a heat exchanger (10), where it is heated,        while the treated stream (7) that has left the fixed bed        “trickle bed” reactor (6) is cooled until it reaches the        operative temperature of the desalter;    -   the non-treated petroleum stream (11), after having recovered        the heat released by the cooling of the stream flow from the        desalter, still needs to reach the optimal reactive temperature        before entering the top of the trickle bed reactor (6).        Afterwards, the non-treated heated petroleum stream (11) goes to        the furnace (4) which increases the temperature of said        non-treated heated petroleum stream (11) to the optimal reactive        temperature;    -   after the above stage, the effluent (5) from the furnace (4)        then enters into the top of a fixed bed reactor (trickle bed)        (6). In this reactor, the stream flows downward and comes into        contact with the heated catalyst, where the removal of the        naphthenic acids then occurs;    -   the treated stream (7) leaves the fixed bed reactor (trickle        bed) (6) at a higher temperature than the desalter. Afterwards,        it is necessary to reduce this temperature to the operational        temperature of the desalter (1). For this, the treated stream        (7) enters into the first heat exchanger (10) where it will be        placed in contact with the non treated petroleum stream (9),        with the purpose of cooling the treated stream (12) to the        temperature of the desalter, and, therefore, acceptable for        entry into the desalter.

EXAMPLE 1

In a Parr reactor, a mixture is made consisting of 700 g from a sampleof Marlim Leste crude oil (TAN=3.2 mg KOH/g of oil) not yet desalted,and 210 g of the spent catalyst without any additional treatments andcoming from an HDT unit. The mixture was warmed until reaching 350° C.and the TAN variation with the time calculated using the ASTM 664method. The results reached are found in the table in FIG. 3.

According to said table, it is clearly discernable that, using the spentcatalyst of HDT/oil ratio of 0.3, after close to 28 minutes, a reductionin TAN of over 84% is obtained as indicated by the arrow (13). Similarresults were obtained when dealing with heavier fraction of the stream.

EXAMPLE 2

A hydrocarbon mixture with a TAN of 2.82 mg KOH/g of oil wascontinuously pumped into a pre-heating system, followed by a pipereactor with a fixed bed containing a spent HR348 catalyst coming froman HDT unit. The hydrocarbon mixture was processed at 350° C., in theabsence of hydrogen and two space velocity conditions were evaluated.After 20 hours, at space velocities of 4 h⁻¹ and 2 h⁻¹, the TAN of thehydrocarbon mixture effluent, calculated by the ASTM 664 method, wasreduced by 62.5% and 64.5%, respectively.

The description made here of the process for reducing acidity inhydrocarbon mixture, the object of the present invention, should beconsidered only as a possibility or possible models, and any particularcharacteristics introduced herein should be understood only as somethingthat was described to facilitate understanding. In this way, they shouldnot in any way be considered as limitations of the invention, which islimited to the scope of the claims that follow.

1. Process for the reduction of acidity in hydrocarbon mixture with hightotal acidity index, through adsorption and the reaction of organicacids on the surface of a catalyst, characterized by the inclusion ofthe following stages: heating of the hydrocarbon mixture to be treated;placing in contact, continually, said hydrocarbon mixture with a fixedbed of spent catalyst coming from a Hydrotreatment unit, at a pressuresuch that after the treatment, the hydrocarbon mixture will be at thenormal pressure of the downstream system; continual withdrawal of thetreated hydrocarbon mixture containing a reduced total acid number (TAN)value of total acidity for later processing in conventional petroleumrefinery units; and disposal of the catalyst at the end of the campaigntime, in the usual way used in conventional Hydrotreatment units. 2.Process for the reduction of the acidity of hydrocarbon mixtures, inaccordance with claim 1, characterized as including hydrocarbon mixturesthat may be chosen from: petroleum products, their fractions andderivatives.
 3. Process to reduce acidity of hydrocarbon mixtures, inaccordance with claim 1, characterized as including hydrocarbon mixturesthat present a total acid number (TAN) that falls within a range ofbetween 1 and 10 mg KOH/g of oil, preferably with a TAN that fallswithin a range of between 1.5 and 8 mg KOH/g of oil.
 4. Process for thereduction of the acidity of hydrocarbon mixtures, in accordance withclaim 1, characterized as including heating of the hydrocarbon mixturesto be treated at temperatures that fluctuate within a range between 240°C. and 400° C., before the desalting stage.
 5. Process for the reductionof the acidity of hydrocarbon mixtures, in accordance with claim 1,characterized as including heating of the hydrocarbon mixtures to betreated at temperatures that fluctuate within a range between 240° C.and 400° C., after the desalting stage.
 6. Process for the reduction ofthe acidity of hydrocarbon mixtures, in accordance with claim 1,characterized as including contact of the hydrocarbon mixture with afixed bed of spent catalyst coming from a Hydrotreatment unit at atemperature within the range of 270° C. and 350° C., preferably at atemperature in the range of between 270° C. and 350° C.
 7. Process forthe reduction of the acidity of hydrocarbon mixtures, in accordance withclaim 1, characterized as having a space velocity in the reactor fallingwithin a range of between 0.25 h⁻¹ and 10 h⁻¹, preferably within a rangeof between 0.5 h⁻¹ and 4 h⁻¹.
 8. Process for the reduction of theacidity of hydrocarbon mixtures, in accordance with claim 1,characterized by a catalyst used in this invention that is refuse or amixture of discarded catalysts from Hydrotreatment units, made oftransition metals, supported in refracting oxides that may be chosenfrom any one of the following: alumina; silica titanium; zirconium; andmixtures of refracting oxides.
 9. Process for the reduction of theacidity of hydrocarbon mixtures, in accordance with claim 1,characterized as having an intermediary stripping stage of the spentcatalyst coming from a Hydrotreatment unit in the presence of an inertgas.
 10. Process for the reduction of the acidity of hydrocarbonmixtures, in accordance with claim 1, characterized as being implementedbefore the desalter.
 11. Process for the reduction of the acidity ofhydrocarbon mixtures, in accordance with claim 1, characterized as beingimplemented after the preflash tower for removal of the light[products].
 12. Process for the reduction of the acidity of hydrocarbonmixtures, in accordance with claim 1, characterized as including aprocess of additional heating of non-treated hydrocarbon mixtures with atreated hydrocarbon mixture, so as to reduce the temperature of thetreated hydrocarbon mixture before they enter the desalter.
 13. Processfor the reduction of the acidity of hydrocarbon mixtures, in accordancewith claim 1, characterized by including a furnace mounted before thereactor so that the reaction temperature necessary for the treatment isattained.